Automobiles are equipped with electronic control units for controlling the various electrical components therein, e.g. electronic fuel injection and anti-lock brake systems. Water and dirt entering the engine compartment from the road, as well as high temperatures, decrease the reliability of electronic control units. Heat, water, and dirt are known to have deleterious effects on the semiconductors which are used in these devices. In order to have adequate heat and water resistance, specially designed semiconductors must be used, which makes the unit very expensive.
One solution has been to mount the electronic control unit in the passenger compartment of the automobile. As shown in FIG. 3, electronic control unit 1 is mounted in car 2 in passenger compartment 2a. The problem with mounting electronic control unit 1 in passenger compartment 2a is that wire harness W/H must be passed from engine compartment 2b into passenger compartment 2a. This requires a long wire harness W/H to pass through panel 2c, which separates passenger compartment 2a from engine compartment 2b. This generates complex operations and increased costs.
Another solution to the problem is to use a protective storage box. As shown in FIG. 4, and discussed in Japanese Patent Application Number 8-275335, electronic control unit 1 is housed in a storage box comprising inner box 3, outer box 4, and upper cover 5. A space is formed between inner box 3 and outer box 4 to allow cooling air to circulate and heat to dissipate. Although the storage box shown in FIG. 4 has good heat radiation characteristics, it has problems with water-tightness. Openings 3a of inner box 3 are covered only by upper cover 5. Thus, if upper cover 5 is damaged, or if water droplets form on its inner wall due to condensation or the like, electronic control unit 1 comes into contact with water, leading to malfunction or damage.